1. Field of the invention
The present invention relates to a drive assist system for raising an alarm when a vehicle moves out from the lane and more particularly to a drive assist system capable of controlling the alarm according to situations.
2. Prior Arts
There is an idea of realizing a safety of a vehicle by positively assisting a driver's operation and a system introducing this idea is a so-called Active Drive Assist (ADA) System. A primary function of the ADA system is to estimate a hazard of a collision with a forward vehicle, a hazard of a contact with an object, a possibility of a moving-out from a lane of a road and the like, based on surrounding information or running conditions of a vehicle and to inform a driver of these hazardous possibilities or to activate various control devices.
There are known apparatuses employing a laser radar and the like to collect surrounding information. Further, the inventor of the present invention proposes, in Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-265547, a technique in which picture images taken by cameras of the scenery in front of the vehicle are processed to recognize road and traffic conditions in the form of three-dimensional information.
A lane moving-out prevention technique which is one of the functions of the ADA system is for informing drivers of hazard by a warning device and the like, when vehicles come close to the lane marker or move out therefrom due to drivers' inadvertent behaviors such as sudden drowsiness falling on drivers or inattentive driving. Various technologies have been developed to prevent the moving-out from the lane.
However, in the real world, there are cases where drivers are required to negotiate roads crowded with pedestrians or parked vehicles and as a result, drivers often move out of lanes to avoid a contact with those pedestrians or parked vehicles.
In order to make this type of the ADA system more practicable, these drivers' intentional behaviors must be discriminated from inadvertent ones as described above to control or suppress the issuance of alarms.
With respect to the ADA system capable of reflecting drivers' intention, Japanese Patent Application Laid-open No. Toku-Kai-Hei discloses a technology wherein an alarm is raised only when the vehicle moves out from the lane without operating the turn signal lever.
However, drivers not always move out from the lane while the turn signal lever is operated. For example, when the vehicle travels on ordinary roads, in a case where some other vehicle or an obstacle jumps out in front of the vehicle, drivers may move out from the lane without having a leeway for operating the turn signal lever. According to the prior art, in such a case, an alarm is raised in the same manner regardless of drivers' intention.
Therefore, in order to make the ADA system more usable, it is required that the warning device of the ADA system is stopped or suppressed (for example, in case of a sound-based warning device, reduce the sound level, change the tone of the sound, stop the sound and the like) according the necessity of the warning.